The present invention relates to a method for treating a single side surface of a metallic sheet, such as a steel sheet, for example, leaving the surface of the other side of the sheet untreated.
There is a demand for supplying steel sheet, for example, with a single side surface having been subjected to an appropriate treatment such as applying to a single side surface a coating of zinc or zinc alloy, or a coating of tin, lead, or other dissimilar metal or alloy. For example, sheet steel galvanized on one surface only presents many advantages in the automobile and appliance industry where it is desired to paint the non-treated surface and leave the treated surface intact to resist corrosion, as it is difficult to obtain a good and smooth painted surface over an anti-corrosion coating of zinc or zinc alloy, for example.
Diverse methods have been proposed in the past for, for example, galvanizing only one surface of a steel sheet such as by welding two steel strips back-to-back at their edge, or by crimping the edges, so as to form a sandwich or laminate which is subjected to an appropriate treatment, such as zinc or zinc alloy hot dipping or electrolytic plating. The edge weld or crimping prevents the molten metal or metal alloy, or the electrolyte, from penetrating between the two sandwiched or laminated strips, with the result that only one surface, the exterior surface of each strip is plated. After treatment, the two strips are separated, generally by shearing off the edges of the sandwiched or laminated strips.
The inconveniences of welding two steel strips back-to-back at their edges are that the heat of welding has a pronounced effect on the metallurgy of the steel, and there is a considerable loss of material resulting from the edge shearing. Another inconvenience resulting from forming a sandwich or laminate of two metallic strips by edge crimping is that the crimp may not provide an effective dam preventing molten metal, or electrolyte, from seeping through the crimp and may cause irregular and random seepage through the edge crimp, thus coating or plating a portion of the surfaces which it is desired to protect.